Following the German occupation of Czechoslovakia in 1939, the Luftwaffe incorporated captured Š-328s into their inventory. The Letov Š-328 only saw limited use by the Luftwaffe during World War II, primarily as a trainer. A small number were also used in the night attack role on the Eastern Front in the Winter of 1942–43.
Bulgaria purchased 62 Letov S-328s from Germany in 1939. OF these, 30 were new built machines manufactured in Czechoslovakia after the German occupation. The others were sourced from stocks seized by Germany. Bulgaria used the S-328s for anti-submarine patrols of the Black Sea flying out of the Sarafovo and Balchik airfields.
Letov sent the Š-128 registered OK-VOT on a demonstration tour of the Baltic states in September 1931. Estonia expressed interest but required several modifications.
To meet the Estonia requirements, the Š-128 received a new landing gear with hydropneumatic shock absorbers and an increased vertical and horizontal tail area. The modified aircraft was redesignated the Š-228. Four Š-228E aircraft were then produced for the Estonian Air Force in 1932. The original prototype aircraft was left in the possession of Letov and in February 1932 now registered OK-VOU it was sent on another demonstration trip to the Baltics, focusing mainly on Finland. It crashed there a month later, but the interest it aroused in Finland gave rise to another version marked Š-328.
The Estonian Š-228s took no part in the Soviet invasion of Estonia in 1940.
